High voltage fuses



March 1o, 1959 P, C, JACOBS, JR 2,877,32l

HIvGH VOLTAGE FUSES Filed June 12, 1957 United States Patent O HIGH VOLTAGE FUSES Philip c. Jacobs, Jr., Newtonvine, Mass., assignor to The `Chase-Shawmut Company, Newburyport, Mass.

Application June 12, 19577, Serial No. 665,294

11 Claims. (Cl. 20d-120) This invention relates to current-limiting fuses, and more particularly to current-limiting fuses for high-voltage circuits. v

Current-limiting fuses are generally filled with a pulverulent fulgurite-forming filler such as quartz sand. The fulgurite formed by fusion of the quartz sand under the heat of the arc incident to blowing of the fuse is a conductor of electricity as long as its temperature is relatively high. The small current still owing through a hot fulgurite formed `in a current-limiting fuse after having interrupted a fault current may gener-ate sufficient heat in the arcing zone of the fuse lto ycause a restrike and concomittant destruction of the fuse, i. e. destruction thereof subsequent to initial successful performance of its duty.

It is one object of this invention to provide currentlimiting fuses applicable for high-voltage circuits which are not subject to theaforementioned serious drawback.

Another object' ofthe invention is to provide currentlimiting fuses the pulverulent arc-quenching filler of which forms a plurality of spaced fulgurites on blowing of the fuse rather than a continuous fulgurite extending along the entire casing of the fuse from terminal to terminal.

it is desirable to provide the fusible elements of highvoltage fuses with means which define along the fusible clement a plurality of spaced points where arc initiation is to occur on yoverloads of inadmissible duration (as distinguished from fault current of short-circuit current proportions). Various means have been devised to achieve this end, yet any of the prior art means is subject to limitations, or disadvantages.

It is, therefore, still another object of the invention to provide improved high-voltage fuses capable of producing multi-breaks at the occurrence of relatively small protracted overloads.

A further object of the invention is to provide highvoltage fuses comprising simple and efficient means for producing blasts of `gas to quench the arcs, or arclets, formed at each of/said plurality of breaks, and to sweep arc products away from the points of arc initiation.

Another object of the invention is to provide highvoltage fuses including a single means for raising the temperature at predetermined spaced points of the fusible element, and for producing an arc-extinguishing gas blast at each of thesespaced points.

Another object of the invention is to provide fuse structures combining the advantages of expulsion fuses with the advantages of current-limiting fuses including a pulverulent fulgurite-forming arc-quenching filler.

These and other objects of the invention and advantages thereof will become more apparent from the following description of preferred embodiments thereof, when taken in connection with the accompanying drawings, in which:

Fig. 1 is a section along 1-1 of Fig. 1a of a currentlimiting fuse embodying theinvention;

Fig. la is a section along liz-1a of Fig. 1;

Fig. 2 illustrates in the same way as Fig. 1 the same 2,877,321 Patented Mar. 10, 19519 ice 2 structure as shown n Figs. 1 and la upon blowing thereof;

Fig. 3 is a section similar to Fig. 2 of a portion of a blown fuse, but showing another modified construction;

Fig. 4 is a section along 4 4 of Fig. 4a of a portion of a modified form of fuse; and

Fig. 4a is a section along ia-'4a of Fig. 4.

Referring now to the drawing, and more particularly Figs. l and la thereof, reference numeral 1 has been applied to indicate a substantially tubular-casing of insulating material as, for instance, a synthetic-resin-glass-cloth laminate. The ends of casing 1 areclosed by terminal elements in the form of caps 2 held in position by any suitable means as, for instance, crimping. Casing 1 accommodates a pulverulent fulgurite-forming arc-quenching filler 3, i. e. a filler which forms a conductive fulgurite under the heat of the arcs formed incident to blowing of the fuse. Reference numeral 4 has been applied to indicate an elongated support for a fusible element or fuse link. This support 4 is made of a refractory material, and may be an extrusion made of a ceramic material. The length of support 4 is substantially equal to the length of casing l, i. e. support 4 is but slightly shorter than casing ll. Numeral 5 indicates a fusible element which may be in the form of a wire or in the form of a ribbon, and which consists preferably of silver. The ends 5a of fusible element 5 are conductively connected to terminal caps 2. To this end caps 2 may be perforated, and ends 5a threaded through the perforations in caps 2 and soldered to caps 2 at the outsides thereof. Support 4 is provided with a plurality of substantially transverse passages 6, and fusible element 5 is threaded through passages 6 Zigzagging back and forth between two of the sides of support 4. Thus fusible element 5 forms a plurality of serially related sections of which passage-enclosed sections alternate with exposed surface sections, i. e. sections situated on thesurface of support 4. f

It will be apparent that when the fuse is carrying current heat dissipation away from the exposed surface sections of fusible element 5 will be considerably higher than away from the passage-enclosed sections thereof. A steep temperature peak will develop approximately at the middle of each passage-enclosed section of the fusible elements. At these points fusing temperature may be reached at the occurrenceof protracted overloads. This then causes formation of series breaks. The products of arcing produced at these breaks tend to escape from passages 6 at both ends thereof. in so doing the products of arcing tendto establish arc-extinguishing blasts. ff the overload is relatively small, less than all passage-enclosed sections of the fusible element will fuse, yet as long as there is a tendency to formation of multibreaks at relatively small current intensities the structure will be able to successfully interrupt relatively small overload eurrents.

At the occurrence of relatively high fault current the fusible element 5 will fuse at all passage-enclosed sections. There will be a rapid burn-back from the points of arc initiation. This burn-back may be so rapid as to establish the impression that all points of fusible element S fuse and vaporize substantially simultaneously. The crosssectional area of each passage 6 is sufficiently small to cause the products of arcing formed upon fusion of fusible element 5 to blast substantially all of filler 3 which may have penetrated into passages 6 out of passages 6. As a result, a plurality of gaseous gaps is formed in the current path inside support 4 at which points the rate of dielectric recovery is relatively high and at which points no conductive fulgurites are formed.

In Fig. 2 reference letter s has been applied to indicate the spacing between the entrances of two adacent passages 6. Passages 6 and their entrances are spaced sufciently in a direction longitudinally of support 4 to normally preclude any merger of the fulgurites 7 formed at the entrances of passages 6. The spacing required to achieve this end can readily be found empirically by appropriate tests.

Fig. 2 shows a fuse upon interruption of a fairly severe fault. The portions of link inside passages 6 have been completely vaporized, leaving passages 6 empty. A fulgurite 7 is formed at both entrances of each passage 6 by the impact of the hot arc products escaping from passages 6 upon the cold quartz sand outside of passages 6. Each fulgurite 7 is separated by a body of non-fused quartz sand 3 from all the other fulgurites 7 inside of casing 1. Portions of the fuse link 5 situated exteriorly of support 4 between adjacent fulgurites 7 have not been fused and vaporized. The non-fused and non-vaporized portion of link 5 is relatively large. Considering a more severe interruption, this portion may well decrease and under excessively severe conditions ultimately all fulgurites 7 might be caused to merge into one single pair of substantially linear fulgurites extending from terminal cap 2 to terminal cap 2. Such a condition should not be permitted to develop since it would mean a reduction of the safety factor inherent in the operation of the fuse, and may be conducive to failure thereof. By proper selection of the spacing of passages 6 any merger of fulgurites 7, even under the most severe interrupting conditions, can readily be avoided.

Referring now to Fig. 3, casing 1 accommodates the pulverulent arc-quenching quartz filler 3 in which the ceramic support 4 for a fusible element (not shown) is submersed. Support 4 is provided with converging passages 6 to accommodate the entire length of a fusible element, i. e. in the embodiment of the invention of Fig. 3 the entire length of the fusible element is enclosed in passages 6', except at the points of intersection between two converging passages 6. At these points the arc products resulting from fusion and vaporization of the fusible element are being discharged into the quartz ller 3, resulting in the formation of fulgurites 7.

The structure of Figs. 4 and 4a is intended to provide increased heat absorption at the arcing zone by an increase of the area of heat exchange between the arc and the pulverulent arc-quenching filler. In Figs. 4 and 4a numeral 1" has been applied to designate a tubular casing housing the refractory support 4 surrounded by the pulverulent fulgurite-forming arc-quenching ller 3". The support 4" forms four ridges 8 and intermediate recesses or cavities 9". Ridges 8" and cavities 9 extend in a direction substantially longitudinally of support 4". Opposite pairs of ridges 8 are connected by passages 6". As clearly shown in Figs. 4 and 4a passages 6" are arranged at different levels and immediately adjacent passages are angularly displaced 90 degrees. Fusible element 5" is threaded through passages 6 as follows: Out of right end of a passage 6" and into rear end of a passage 6" at the next lower level; out of front end of passage 6" at the same level and into left end of passage 6 at the next lower level; etc. The portions of fusible element 5" extending between two adjacent ridges 8 and spanning the recess or groove 9 therebetween is enveloped by arc-quenching filler 3, i. e. arcqucnching ller 3 surrounds the entire surface of these portions of fusible element 5". The support of fusible element 5" is limited to a number of spaced points where it physically engages support 4 and ller 3" has access to the exterior portion of fusible element 5" except the points thereof resting against support 4".

It will be apparent from the foregoing that the structure of Fig. 3 differs from the structure shown in the other figures inasmuch as in the structures shown in the other figures a relatively substantial length of the fusible element 5 is situated outside of passages or tunnels 6 where heat dissipation is relatively large. In the structure of Fig. 3 there is no significant external cooling action of the fusible element (not appearing in Fig. 3 since that figure shows the fuse in the condition in which it is after blowing and vaporization of the fusible element), but the relatively long tunnels 6 control heat dissipation in such a way as to result in high spot-temperatures near the center of each tunnel 6. It will also be apparent from the foregoing that I provide thermal means for causing formation of a lirst plurality of serially related spaced sections on fusible element 5 tending to assume a relatively high temperature when the fuse is carrying current alternating with a second plurality of spaced sections tending to assume a relatively low temperature when the fuse is carrying current. Said thermal means include the body 3 of pulverulent quartz filling the radially outer area of casing 1, and said thermal means further include support or mandrel 4 of refractory material deiining tunnels 6 accommodating said first plurality of sections of the fusible element 5. The radially outer ends of some of tunnels 6 have a predetermined spacing in a direction longitudinally of mandrel or support 4 suffrciently large to preclude merger of fulgurites formed at spaced ends of tunnels 6.

While there have been describedl what are at present considered to be preferred embodiments of the invention, it will be understood that various modifications may be made therein which are within the true spirit and scope of the invention as dened in the appended claims.

I claim:

l. In a current-limiting fuse the combination of a substantially tubular casing of insulating material, an elongated support of a refractory material arranged inside said casing, a plurality of passages extending across said support, a fusible element of silver threaded through said plurality of passages, a pair of terminal elements closing said casing conductively interconnected by said fusible element, a pulverulent quartz ller filling the space defined by the inner surface of said casing and the outer surface of said support, the heat dissipating properties of said support, of said fusible element and of said ller being so correlated as to cause on occurrence of overload currents formation of a plurality of points of relatively elevated temperature and eventual arc initiation along said fusible element each in one of said plurality of passages, and the cross-sectional area of each of said plurality of passages being sufficiently small to cause upon said eventual arc initiation a plurality of opposite blasts sweeping said quartz filler out of said plurality of passages.

2. In a current-limiting fuse the combination of a substantially tubular casing of insulating material, an elongated support of a refractory material arranged inside said casing, a plurality of passages extending across said support, a fusible element of silver zig-zagging through said plurality of passages and engaging with a substantial portion of the total length thereof the outer surface of said support, a pair of terminal elements closing said casing conductively interconnected by said fusible element, a pulverulent quartz filler lling the space defined by the inner surface of said casing and the outer surface of said support, the cross-sectional area of each of said plurality of passages being sufficiently small to blast said ller upon fusion of said fusible element inside of said plurality of passages out of said plurality of passages.

3. In a current-limiting fuse the combination of a substantially tubular casing of insulating material, a pair of terminal elements closing the ends of said casing, an elongated unitary support of a refractory material arranged inside of said casing, a plurality of relatively narrow tunnels extending through said support, a fusible element conductively interconnecting said pair of terminal elements mounted on said support, said fusible elements being threaded through said plurality of tunnels to form a plurality of exposed surface sections of substantial length alternating with tunnel-enclosed sections, and a pulverulent fulgurite-forming arc-quenching ller in physical engagement with said surface sections of said fusible element.

4. In a current-limiting fuse the combination ofasubstantially tubular casing of insulating material, a pair of terminal elements closing said casing, a pulverulent fulgurite-forming arc-quenching filler inside said casing, a

fusible element conductively interconnecting said pair tending to assumea relatively'.highzlemperature when said fuse iscarr-ying current alternating with a plurality of spaced sections situated outside said plurality of passages tending to assume a relatively low temperature when said fuse is carrying current, and the cross-sectional area of each of said -plurality of passages being sufficiently small to cause products of arcing formed upon fusion of said fusible element and blasting out of said plurality of passages to keep said plurality of passages substantially free from said filler.

5. In a current-limiting fuse the combination of a substantially tubular casing of insulating material, a pair of terminal elements closing said casing, a pulverulent quartz filler inside said casing, a fusible element of silver conductively interconnecting said pair of terminal elements, an elongated support formed of a unitary member of refractory material submerged in said filler supporting said fusible element, said support having a plurality of substantially transverse tunnel passages and said fusible element being threaded through said plurality of tunnel passages in a zig-zag path in such a Way that said fusible 9 element forms a plurality of serially related spaced sec tions situated inside said plurality of passages tending to assume a relatively high temperature when said fuse is carrying current alternating with a plurality of spaced sections situated outside said plurality of passages tending to assume a relatively low temperature when said fuse is carrying current, and the cross-sectional area of each of said plurality of tunnel passages being suiiiciently small to cause products of arcing formed upon fusion of said fusible element to blast substantially all said filler that may have entered said plurality of passages out of said plurality of passages.

6. In a current-limiting fuse the combination of a substantially tubular casing of insulating material, a pair of terminal elements closing said casing, a pulverulent fulgurite-forming arc-quenching filler filling said casing,

;a fusible element of silver conductively interconnecting `said pair of terminal elements, a support of a refractory material submersed in said filler supporting said fusible clement, said support having lateral projections forming recesses therebetween, said projections supporting said fusible element at spaced points only and said recesses permitting substantially full access of said filler to the yportions of said fusible element situated between said spaced points, said support having a plurality of sub- :stantially transverse tunnel passages extending between :said projections, and said fusible element being threaded through said plurality of tunnel passages substantially in a zig-zag path.

7. In a current-limiting fuse the combination of a substantially tubular casing of insulating material, a pair of terminal elements closing said casing, a pulverulent quartz filler inside said casing, a fusible element of silver in said owing conductively interconnecting said pair of terminal elements, a support of refractory material submersed in said filler supporting said fusible element, said support having a plurality of ridges extending in a direction substantially longitudinally thereof and forming recesses therebetween, said ridges supporting said fusible element only at spaced points thereof and said fusible element ,spanning said recesses .whereby y,substantially full access of saidller to saidv fusible element is.P.rmitted at the points thereof where said fusible element is spanning said recesses, said support having a plurality ,of passages extendingvbetween said ridges, and-said fusible element being threaded through said pluralityof passages substantially in a zig-zag path.

8. In a current-limiting fuse the combination of a substantially tubular casing of insulating material, a pair of terminal elements closing said casing, a pulverulent quartz filler inside said casing, a fusible element conductively interconnecting said pair-offiterminal elements, a support of refractory material for lsaid fusible element arranged inside said casing, said support havinga plurality of ridges extending in a direction substantially longitudinally thereof and forming recesses therebetween, said ridges supporting said fusible `.element onlytat spaced points thereof and said recesses permitting substantially free accessof said tillertoportionsof said fusible element spanning said recesses, said support having a plurality of `substantially transverse tunnel passages extending between said plurality of ridges and said fusible element being threaded through said plurality of tunnel passages in a zig-zag path, the cross-sectional area of each of said plurality of tunnel passages being sufficiently small to cause products of arcing formed upon fusion of said fusible element to blast substantially all of said filler which may have penetrated into said plurality of passages out of said plurality of passages, and some of the entrances to said plurality of passages being spaced in a direction longitudinally of said support to preclude merger of fulgurities formed at said entrances upon fusion of said fusible element.

9. In a current-limiting fuse the combination of a substantially tubular casing of insulating material, a mandrel of refractory material arranged coaxially inside of said casing, a plurality of tunnels extending transversely across said mandrel, a fusible element of silver engaging the outer surface of said mandrel and threaded through said plurality of tunnels, a pulverulent quartz filler filling the space defined by the inner surface of said casing and the outer surface of said mandrel, the ratio of the length of said fusible element situated outside said plurality of tunnels where heat dissipation occurs at a relatively rapid rate to the total length of said fusible element situated inside said plurality of tunnels where heat dissipation occurs at a relatively small rate being such as to form points of initial fusion inside said plurality of tunnels when said fuse is carrying overload currents of inadmissible duration, and the cross-sectional area of each of said plurality of tunnels being sufliciently small to blast upon said initial fusion of said fusible element substantially all of said quartz ller penetrated into said plurality of tunnels out of said plurality of tunnels.

l0. A current-limiting fuse comprising a substantially tubular casing of insulating material, a pair of terminal elements closing the ends of said casing, a fusible element of silver inside said casing conductively interconnecting said pair of terminal elements, thermal means for causing formation of a first plurality of serially related spaced sections on said fusible element tending to assume a relatively high temperature when said fuse is carrying current alternating with a second plurality of spaced sections tending to assume -a relatively low temperature when said fuse is carrying current, said thermal means including a unitary mandrel coaxially arranged inside of and spaced from said casing, said mandrel defining a plurality of transverse tunnels spaced in a direction longitudinally of said mandrel and accommodating said first plurality of sections of said fusible element and said thermal means further including a pulverulent quartz liller filling said plurality of tunnels and submersing said mandrel, the cross-sectional area of each of said plurality of tunnels being sufficiently small to cause products of -arcing formed upon fusion of said fusible element to blast 7 substantially all of said ller penetrated into said plurality of tunnels out of said plurality of tunnels whereby a substantially fulgurite-free gaseous break is formed in each of said plurality of tunnels.

1l. A current-limiting fuse comprising a substantially tubular casing of insulating material, a pair of terminal elements closing the ends of said casing, a fusible element of silver inside said casing conductively interconnecting said pair of terminal elements, thermal means for causing formation of a first plurality of serially related spaced sections on said fusible element tending to assume a relatively high temperature when said fuse is carrying current alternating with a second plurality of spaced sections tending to assume a relatively low temperature When said fuse is carrying current, said thermal means including a body of pulverulent quartz filling the radially outer area of said casing and said thermal means further including a mandrel of refractory material coaxially arranged inside of said casing and submersed in said body of pulverulent quartz, said mandrel having a plurality of '30 2,571,492

transverse tunnels accommodating said rst plurality of spaced sections of said fusible element, the outer ends of some of said plurality of tunnels having a predetermined spacing in a direction longitudinally of said mandrel, the crosssectional area of each of said plurality of tunnels being proportioned to establish upon fusion of said rst plurality of spaced sections of said fusible element a plurality of blasts tending to remove substantially all of said body of pulverulent quartz penetrated into said plurality of tunnels out of said plurality of tunnels, and said predetermined spacing being sufliciently large to preclude merger of fulgurites formed at longitudinally spaced ends of said plurality of tunnels.

References Cited in the tile of this patent UNITED STATES PATENTS Fellenberg Feb. 27, 1906 Thommen et al lan. 28, 1941 Schultz Oct. 16, 1951 

